1. Field of the Invention
The present invention relates to a method for determining the absolute position of a movable component within a vehicle chassis.
2. Description of the Related Art
In motor vehicles, the demand for adjustable damping and adjustable suspension forces and for ride leveling is increasing. For ride leveling, the main parameter to be determined is the stationary or dynamic deviation from a specified normal or reference position. The standard method of determining the stationary or dynamic deviation is based on the installation of a transmission linkage between an axle component and the vehicle body, so that the relative movement between the vehicle axle and the body may be used as a signal for adjusting the level of the body. A significant disadvantage of this principle is that these types of mechanical solutions must always be adjusted as part of the installation process.
An alternative method for determining the stationary or dynamic deviation from the normal or reference position is to determine an operating position of a vibration damper, which is connected to the chassis. For this purpose, an inductive measuring arrangement may be provided between the piston rod and the cylinder of a vibration damper. This requires magnets to be installed inside the piston rod, for example, which means that the piston rod must be fabricated of austenitic steel, which considerably increases the cost of the piston rod. In addition, a certain amount of space is required to accommodate the magnets inside the piston rod to ensure a sufficiently strong signal. A minimum wall thickness of the piston rod is required surrounding the magnets in the piston rod. However, the required minimum wall thickness may cause the diameter of the piston of the piston rod to be too large for many smaller, lighter vehicles.
Numerous attempts have been made to determine the position of the piston rod using a mark on the piston rod in conjunction with a read sensor. So that an absolute position may be measured, the mark must be unmistakable. In addition, the mark must avoid producing a negative influence on the seal of the piston rod of the vibration damper, because otherwise the service life of the unit would be reduced.